1. Technical Field of the Invention
The present invention relates to a system for sensing angular and linear motion, and more particularly, to an optical encoder that tracks angular and linear position, velocity, and direction.
2. Description of the Related Art
Many technologies track mechanical motion. Some technologies track motion by sensing light. Photoelectric encoders, for example, employ a light source, a code wheel, and light detectors to track the motion of an object like a shaft by sensing modulated light. The light source emits a beam of light in the direction of the code wheel. The code wheel interrupts the beam of light at a frequency that correlates to the rotation of the shaft. The portion of light passing through the code wheel is detected and then converted into electrical signals by light detectors.
Unfortunately, some photoelectric encoders cannot be adapted to small electromechanical technologies. A miniature motor, for example, may use a code wheel that has densely compact transparent and opaque segments to provide a useful resolution.
A known approach that may be practiced with these technologies is described in U.S. Pat. No. 4,691,101 assigned to Hewlett Packard. This approach uses light detectors positioned immediately adjacent to one another to track angular motion. Unfortunately, close arrangements of light detectors can be susceptible to crosstalk created by the diffusion of light through the code wheel, the internal reflection of light within the encoder itself, or the movement of charged particles (e.g. electrons) from one detector to another. Additional circuitry may thus be needed to compensate for this condition, which adds additional parts and expenses to the device and complicates assembly.
The invention provides a system for sensing linear and angular motion. The system comprises a light source, a transducing member, and a modulating member having a track of translucent and opaque regions positioned between the light source and the transducing member. The transducing member includes optical receivers spaced across a width greater than or equal to the combined widths of three translucent and three opaque regions. The optical receivers, which can be interlaced across the transducing member, generate a plurality of output signals that may form at least one output channel signal.
The system may further include a second track of translucent and opaque regions and a second transducing member. The second transducing member includes a second plurality of optical receivers, which can be interlaced across the transducing member, to generate a plurality of signals that may be used to generate at least one index signal.
The alignment and design of the transducing members minimize adjacent interference or crosstalk to which a close alignment of light detectors can be otherwise susceptible. Moreover, insignificant mechanical or optical misalignments will not affect the system of the invention because the spaced-apart relationship of the optical receivers has a wide tolerance. In addition, the system uses a small number of parts that simplify assembly. This may be particularly important when used with miniature technologies.